Keyboard shortcuts help you save time since you never have to take your hands off the keyboard to use the mouse. You’ll need a Standard 101/102-Key or Natural PS/2 Keyboard to use the shortcuts. To turn these case-sensitive shortcuts on or off, click Settings, and then pick an option next to Keyboard shortcuts.

http://mail.google.com/support/bin/answer.py?ctx=%67mail&hl=en&answer=6594